Publications (73) View all
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Article: Four-body interaction energy for compressed solid krypton from quantum theory.
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ABSTRACT: The importance of the four-body contribution in compressed solid krypton was first evaluated using the many-body expansion method and the coupled cluster theory with full single and double excitations plus perturbative treatment of triples. All different four-atom clusters existing in the first- and second-nearest neighbor shells of face-centered cubic krypton were considered, and both self-consistent-field Hartree-Fock and correlation parts of the four-body interaction were accurately determined from the ambient conditions up to eightfold volume compression. We find that the four-body interaction energy is negative at compression ratio lower than 2, where the dispersive forces play a dominant role. With increasing the compression, the four-body contribution becomes repulsive and significantly cancels the over-softening effects of the three-body potential. The obtained equation of state (EOS) was compared with the experiments and the density-functional theory calculations. It shows that combination of the four-body effects with two- and three-body interactions leads to an excellent agreement with EOS measurements throughout the whole experimental range 0-130 GPa, and extends the prediction to 300 GPa.The Journal of chemical physics 07/2012; 137(4):044108. · 3.09 Impact Factor -
Article: A Catalytic Study of the Modified Coal Gasification Process to Produce Clean Hydrogen Gas
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ABSTRACT: A catalytic study was performed on the following proposed modified coal gasification reaction: NaOH(s) + C(s) +H 2 O (g) = Na 2 CO 3 (s) + H 2 (g). Our study reveals that in the presence of 2 h ball milled Raney nickel (average crystallite size of 209 Å) this reaction is completed at 500 0 C in 120 minutes. X-ray diffraction technique is used for the characterization of the catalysts. Catalyst's surface morphology is analysed by using scanning electron microscope. From a study of the surface morphology and activity of the used catalysts, a direct correlation of coal particle size with the reaction kinetics has been established. The findings reveal that the globular particles have better catalytic effect than flaky disk shaped particles.CheM. 01/2012; 2(1):20-26. -
Article: A modified method for production of hydrogen from methane
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ABSTRACT: The steam–methane-reformation (SMR) reaction has been modified by including sodium hydroxide in the reaction. It is found that the reaction: 2NaOH1CH 4 1H 2 O 5 Na 2 CO 3 14H 2 takes place at much lower temperatures (300–6001C) than the SMR reaction (800–12001C). The reaction rate is enhanced with a nickel catalyst. We have studied the effect of variously ball-milled nickel on the reaction rate and determined the optimum particle size of the catalyst. Best results were achieved by grinding the catalyst for 2 h. Prolonged ball milling caused the nickel platelets to coalesce and grow in size decreasing the reaction rate.International Journal of Energy Research 01/2011; · 2.12 Impact Factor -
Article: An extended high pressure-temperature phase diagram of NaBH4.
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ABSTRACT: We have studied the structural stability of NaBH(4) under pressures up to 17 GPa and temperatures up to 673 K in a diamond anvil cell and formed an extended high P-T phase diagram using combined synchrotron x-ray diffraction and Raman spectroscopy. Even though few reports on phase diagram of NaBH(4) are found in current literature, up to our knowledge this is the first experimental work using diamond anvil cell in a wide pressure/temperature range. Bulk modulus, its temperature dependence, and thermal expansion coefficient for the ambient cubic phase of NaBH(4) are found to be 18.76(1) GPa, -0.0131 GPa K(-1), and 12.5x10(-5)+23.2x10(-8) T/K, respectively. We have also carried out Raman spectroscopic studies at room temperature up to 30 GPa to reinvestigate the phase transitions observed for NaBH(4). A comparative symmetry analysis also has been carried out for different phases of NaBH(4).The Journal of chemical physics 09/2009; 131(7):074505. · 3.09 Impact Factor -
Article: High-Pressure Investigation on Calcium Borohydride
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ABSTRACT: Structural properties of calcium borohydride, Ca(BH4)2, containing α and β polymorphs are investigated under pressure by in situ synchrotron X-ray diffraction up to 13 GPa and by Raman spectroscopy up to 25 GPa. Results show that the β phase transforms to a highly disordered structure above 10.2 GPa, whereas the α phase is stable in the pressure range studied. Rietveld analysis of the X-ray diffraction pattern collected at ambient conditions shows that the α phase is an orthorhombic F2dd structure with lattice parameters a = 8.82(7) Å, b = 13.05 (10) Å, c = 7.404(5) Å, and V = 851.8(10) Å3 (64.13 cm3/mol). The β phase was checked for all the suggested tetragonal structures, and the best match is obtained with space group P42/m; the lattice parameters are a = 6.88(4) Å, c = 4.32(5) Å, and V = 204.82(18) Å3 (61.68 cm3/mol). Pressure volume data obtained for α-Ca(BH4)2 are fitted with the third-order Birch−Murnaghan equation of state that yields a bulk modulus value of K0 = 22.95(4) GPa with K0′ = 2.63(0.5).08/2009;
